Tear in odd part of the eye (6)
I believe the answer is:
retina
'part of the eye' is the definition.
('retina' is part of 'eye')
'tear in odd' is the wordplay.
'odd' indicates anagramming the letters.
'tear'+'in'='tearin'
'tearin' anagrammed gives 'RETINA'.
(Other definitions for retina that I've seen before include "Sensitive layer in eye" , "Eye's membrane" , "Light-sensitive membrane in the eye" , "Membrane covering the back of the eyeball" , "Membrane that can become detached" .)